The present invention relates to a machine tool for grinding or cutting blade crests and rake faces in the hemispherical portion of a bar-shaped workpiece such as an end mill having a hemispherical end.
Generally, the blades cannot always be shaped as one likes them to be when a crude material or an end mill having a square-cut end is to be made into an end mill having a hemispherical end.
In addition, many of the end mills having ordinary or hemispherical ends have spiral blades as shown in FIGS. 10 and 11 so as to have good performance in a metal-cutting operation. In case of the end mills having hemispherical ends, it has been a common practice to finish the shank A and the hemispherical portion B separately from each other, because it has been difficult to finish them by a continuous process. Especially, the following disadvantages are caused by a tooth rest which is applied to the rake faces b when the hemispherical portion B is to be ground for reuse:
1. Inflection points or undercuts are liable to be formed in the blade faces at the junction between the shank and the hemispherical portion.
2. The hemispherical portion cannot be precisely ground, because the tooth rest easily slips off the end portion of an end mill having a hemispherical end.
3. Because of the above-mentioned disadvantages, precision in grinding depends largely on the skillfulness of a worker.